US20110103118A1 - Non-isolated dc-dc converter assembly - Google Patents
Non-isolated dc-dc converter assembly Download PDFInfo
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- US20110103118A1 US20110103118A1 US12/917,879 US91787910A US2011103118A1 US 20110103118 A1 US20110103118 A1 US 20110103118A1 US 91787910 A US91787910 A US 91787910A US 2011103118 A1 US2011103118 A1 US 2011103118A1
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
- H02M3/00—Conversion of dc power input into dc power output
- H02M3/02—Conversion of dc power input into dc power output without intermediate conversion into ac
- H02M3/04—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters
- H02M3/10—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
- H02M3/145—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal
- H02M3/155—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only
- H02M3/156—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only with automatic control of output voltage or current, e.g. switching regulators
- H02M3/158—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only with automatic control of output voltage or current, e.g. switching regulators including plural semiconductor devices as final control devices for a single load
Definitions
- the present disclosure relates to a non-isolated DC-DC converter assembly, such as a non-isolated DC-DC converter assembly which is suitable for use with a photovoltaic cell, for example.
- PV photovoltaic
- the isolated inverters allow the photovoltaic panel terminal to be grounded, which is mandatory in some countries due to safety issues relating to leakage current. Grounding the negative photovoltaic panel terminal is also advantageous because it alleviates degradation problems of the photovoltaic panels.
- the presence of the transformer is required when some photovoltaic cell technologies, e.g. thin-film, are employed.
- this extra component e.g., the transformer, when operating at a low frequency, increases the overall volume, weight and cost of the system.
- non-isolated PV inverters require a dedicated topology either on the dc-dc converter side or on the inverter side.
- a known photovoltaic inverter assembly includes a boost converter connected to a full-bridge inverter.
- the boost converter boosts the voltage generated by a photovoltaic string to a level which is necessary for the inverter to transfer the power to the grid.
- the boost converter has advantages, such as a low number of components and simplicity, it has some disadvantages with regard to the connection with the above-mentioned photovoltaic inverter assembly. If the full-bridge inverter operates under a unipolar modulation, which has a higher efficiency as compared to bipolar modulation, a parasitic capacitance existing between the negative terminal of the photovoltaic string and ground creates a path to a common-mode current to circulate. This common-mode current will superimpose the load current causing EMI, safety and degradation problems.
- An exemplary embodiment provides a non-isolated DC-DC converter assembly which includes a positive input terminal, a negative input terminal, a positive output terminal, and a negative output terminal.
- the exemplary DC-DC converter assembly includes a boost converter having a first input terminal, a second input terminal, a first output terminal and a second output terminal.
- the exemplary DC-DC converter assembly also includes an intermediate output terminal, and a ⁇ uk converter, which includes a first input terminal, a second input terminal, a first output terminal and a second output terminal.
- the first input terminal of the boost converter and the second input terminal of the ⁇ uk converter are conductively connected to the positive input terminal.
- the second input terminal of the boost converter and the first input terminal of the ⁇ uk converter are conductively connected to the negative input terminal.
- the first output terminal of the boost converter is conductively connected to the positive output terminal.
- the second output terminal of the ⁇ uk converter is conductively connected to the negative output terminal.
- the second output terminal of the boost converter and the first output terminal of the ⁇ uk converter are conductively connected to the intermediate output terminal.
- the negative input terminal and the intermediate output terminal are configured to be grounded.
- FIG. 1 shows a known boost converter
- FIG. 2 shows a known ⁇ uk converter
- FIG. 3 shows an exemplary embodiment of a non-isolated DC-DC converter assembly connected to a photovoltaic cell, according to an embodiment of the present disclosure
- FIG. 4 shows a simplified circuit diagram of a solar power station including the exemplary converter assembly of FIG. 3 .
- Exemplary embodiments of the present disclosure provide a non-isolated dc-dc converter which allows grounding the negative terminal of the photovoltaic modules, avoiding any safety or degradation issue caused by leakage current flowing in existing parasitic capacitors.
- the non-isolated DC-DC converter assembly includes a boost converter and a ⁇ uk converter connected together in a specific way.
- the non-isolated DC-DC converter assembly allows for grounding of a source and load at the same time.
- a complete adjustability of the output voltage of the non-isolated DC-DC converter is achieved.
- the DC-DC converter assembly of the disclosure has current source input characteristic, whereby the current absorbed from the power supply is continuous.
- the converter assembly according to exemplary embodiments of the present disclosure can be installed using any kind of photovoltaic cell technologies without of the drawback of low efficiency, large volume and high cost associated with isolated photovoltaic converters.
- the possibility of grounding the power supply and the load at the same time allows removing the bulky transformer while still avoiding any EMI aspects caused by the presence of a common-mode current flowing through parasitic components.
- FIG. 1 shows a conventional boost converter configured to step up input voltage into higher output voltage.
- the boost converter includes an inductor L 1 ′, a diode D 1 ′ and a controllable switch S 1 ′.
- the boost converter has a first input terminal BCI 1 ′, a second input terminal BCI 2 ′, a first output terminal BCO 1 ′ and a second output terminal BCO 2 ′.
- the input direct voltage is inputted through the first input terminal BCI 1 ′ and the second input terminal BCI 2 ′.
- the first input terminal BCI 1 ′ is a positive terminal
- the second input terminal BCI 2 ′ is a negative terminal.
- the output voltage is present between the first output terminal BCO 1 ′ and the second output terminal BCO 2 ′.
- the first output terminal BCO 1 ′ is a positive terminal
- the second output terminal BCO 2 ′ is a negative terminal.
- the inductor L 1 ′ and the diode D 1 ′ are connected in series between the first input terminal BCI 1 ′ of the boost converter and the first output terminal BCO 1 ′ of the boost converter.
- the cathode of the diode D 1 ′ is connected to the first output terminal BCO 1 ′.
- the collector of the controllable switch S 1 ′ is connected between the inductor L 1 ′ and the anode of the diode D 1 ′, and the emitter of the controllable switch S 1 ′ is connected between the second input terminal BCI 2 ′ and the second output terminal BCO 2 ′.
- the second input terminal BCI 2 ′ and the second output terminal BCO 2 ′ are connected with a conductor having neither active nor passive components. Therefore, the second input terminal BCI 2 ′ and the second output terminal BCO 2 ′ are, in operating conditions, substantially at the same electric potential.
- FIG. 2 shows a known ⁇ uk converter.
- the ⁇ uk converter is capable of stepping up and stepping down its input voltage.
- the ⁇ uk converter includes inductors L 2 ′ and L 3 ′, a diode D 2 ′, a controllable switch S 2 ′, and capacitors C 2 ′ and C 3 ′.
- the ⁇ uk converter has a first input terminal CCI 1 ′, a second input terminal CCI 2 ′, a first output terminal CCO 1 ′ and a second output terminal CCO 2 ′.
- the input direct voltage is inputted through the first input terminal CCI 1 ′ and the second input terminal CCI 2 ′.
- the output voltage is present between the first output terminal CCO 1 ′ and the second output terminal CCO 2 ′.
- the ⁇ uk converter of FIG. 2 is an inverting converter, which means that the output voltage is negative with respect to the input voltage. This means that if an operator wants the first output terminal CCO 1 ′ of the ⁇ uk converter to be the positive one, then the second input terminal CCI 2 ′ must be connected to a higher electrical potential than the first input terminal CCI 1 ′ of the ⁇ uk converter.
- the inductor L 2 ′, the capacitor C 3 ′ and the inductor L 3 ′ are connected in series between the second input terminal CCI 2 ′ of the ⁇ uk converter and the second output terminal CCO 2 ′ of the ⁇ uk converter such that the capacitor C 3 ′ is located electrically between the inductor L 2 ′ and the inductor L 3 ′.
- the inductor L 2 ′ is connected between the second input terminal CCI 2 ′ and the capacitor C 3 ′, and the inductor L 3 ′ is connected between the second output terminal CCO 2 ′ and the capacitor C 3 ′.
- a collector of the controllable switch S 2 ′ is connected between the inductor L 2 ′ and the capacitor C 3 ′, and the emitter of the controllable switch S 2 ′ is connected between the first input terminal CCI 1 ′ and the first output terminal CCO 1 ′.
- the first input terminal CCI 1 ′ and the first output terminal CCO 1 ′ of the ⁇ uk converter are connected with a conductor having neither active nor passive components. Therefore, the first input terminal CCI 1 ′ and the first output terminal CCO 1 ′ are, in operating conditions, substantially at the same electric potential.
- the anode of the diode D 2 ′ is connected between the capacitor C 3 ′ and the inductor L 3 ′.
- the cathode of the diode D 2 ′ is connected between the first input terminal CCI 1 ′ and the first output terminal CCO 1 ′.
- the capacitor C 2 ′ is connected between the first output terminal CCO 1 ′ and the second output terminal CCO 2 ′. Therefore the voltage of the capacitor C 2 ′ is equal to the output voltage of the ⁇ uk converter.
- FIG. 3 shows a non-isolated DC-DC converter assembly according to an exemplary embodiment of the present disclosure connected to a photovoltaic cell means (PVM) having a photovoltaic cell CPV.
- the photovoltaic cell CPV is configured to convert solar energy into direct current (DC).
- the photovoltaic cell CPV is configured to generate a direct voltage u in , which is the input voltage of the non-isolated DC-DC converter assembly.
- the photovoltaic cell CPV can be based on any known photovoltaic cell technology.
- the converter assembly includes features of the boost converter shown in FIG. 1 and the ⁇ uk converter shown in FIG. 2 .
- the converter assembly is a combination of the boost converter shown in FIG. 1 and the ⁇ uk converter shown in FIG. 2 .
- the converter assembly has a positive input terminal IT 1 , a negative input terminal IT 2 , a positive output terminal OT 1 and a negative output terminal OT 2 .
- the input voltage of the converter assembly is present between the positive input terminal IT 1 and the negative input terminal IT 2 .
- the boost converter and the ⁇ uk converter are connected such that the output voltage u out of the converter assembly present between the positive output terminal OT 1 and the negative output terminal OT 2 is substantially a sum of the absolute values of output voltages of the boost converter and the ⁇ uk converter.
- the non-isolated DC-DC converter assembly of FIG. 3 includes all the components in the boost converter of FIG. 1 and in the ⁇ uk converter of FIG. 2 .
- Reference signs used in FIG. 3 correspond to those used in FIGS. 1 and 2 with the exception that apostrophes (') have been removed.
- the boost converter of FIG. 3 has a first input terminal BCI 1 , a second input terminal BCI 2 , a first output terminal BCO 1 and a second output terminal BCO 2 .
- the output voltage u 1 of the boost converter is present between the first output terminal BCO 1 and the second output terminal BCO 2 .
- the ⁇ uk converter of FIG. 3 has a first input terminal CCI 1 , a second input terminal CCI 2 , a first output terminal CCO 1 and a second output terminal CCO 2 .
- the output voltage u 2 of the ⁇ uk converter is present between the first output terminal CCO 1 and the second output terminal CCO 2 .
- the output voltage u out of the non-isolated DC-DC converter assembly of FIG. 3 is a sum of the output voltage u 1 of the boost converter and the output voltage u 2 of the ⁇ uk converter.
- the first input terminal BCI 1 of the boost converter and the second input terminal CCI 2 of the ⁇ uk converter are conductively connected to the positive input terminal IT 1 such that, in operating situations, the first input terminal BCI 1 , the second input terminal CCI 2 , and the positive input terminal are at the same electric potential.
- the second input terminal BCI 2 of the boost converter and the first input terminal CCI 1 of the ⁇ uk converter are conductively connected to the negative input terminal IT 2 such that, in operating situations, the second input terminal BCI 2 , the first input terminal CCI 1 , and the negative input terminal IT 2 are at the same electric potential.
- the first output terminal BCO 1 of the boost converter is conductively connected to the positive output terminal OT 1 such that, in operating situations, the first output terminal BCO 1 and the positive output terminal OT 1 are at the same electric potential.
- the second output terminal CCO 2 of the ⁇ uk converter is conductively connected to the negative output terminal OT 2 such that, in operating situations, the second output terminal CCO 2 and the negative output terminal OT 2 are at the same electric potential.
- the converter assembly of FIG. 3 has an intermediate output terminal OT 3 , which is conductively connected to the second output terminal BCO 2 of the boost converter and the first output terminal CCO 1 of the ⁇ uk converter. Since there are neither active nor passive components between the intermediate output terminal OT 3 and the negative input terminal IT 2 , these two terminals are, in operating situations, at the same electric potential.
- the boost converter of FIG. 3 includes a first inductor L 1 , a first diode D 1 , a first controllable switch S 1 and a first capacitor C 1 .
- the first inductor L 1 and the first diode D 1 are connected in series between the first input terminal BCI 1 of the boost converter and the first output terminal BCO 1 of the boost converter.
- the cathode of the first diode D 1 is connected to the first output terminal BCO 1 of the boost converter.
- the first controllable switch S 1 is located electrically between a point situated electrically between the first inductor L 1 and the first diode D 1 , and a point situated electrically between the second input terminal BCI 2 of the boost converter and the second output terminal BCO 2 of the boost converter.
- the collector of the first controllable switch S 1 is connected between the first inductor L 1 and the anode of the first diode D 1 .
- the first capacitor C 1 is connected between the first output terminal BCO 1 of the boost converter and the second output terminal BCO 2 of the boost converter.
- the ⁇ uk converter of FIG. 3 includes a second inductor L 2 , a third inductor L 3 , a second diode D 2 , a second controllable switch S 2 , a second capacitor C 2 and a third capacitor C 3 .
- the second inductor L 2 , the third capacitor C 3 and the third inductor L 3 are connected in series between the second input terminal CCI 2 of the ⁇ uk converter and the second output terminal CCO 2 of the ⁇ uk converter such that the third capacitor C 3 is located electrically between the second inductor L 2 and the third inductor L 3 .
- the second controllable switch S 2 is located electrically between a point situated electrically between the second inductor L 2 and the third capacitor C 3 , and a point situated electrically between the first input terminal CCI 1 of the ⁇ uk converter and the first output terminal CCO 1 of the ⁇ uk converter.
- the collector of the second controllable switch S 2 is connected between the second inductor L 2 and the third capacitor C 3 .
- the second diode D 2 is located electrically between a point situated electrically between the third capacitor C 3 and the third inductor L 3 , and a point situated electrically between the first input terminal CCI 1 of the ⁇ uk converter and the first output terminal CCO 1 of the ⁇ uk converter.
- the anode of the second diode D 2 is connected between the third capacitor C 3 and the third inductor L 3 .
- the cathode of the second diode D 2 is connected between the first input terminal CCI 1 and the first output terminal CCO 1 .
- the second capacitor C 2 is located electrically between the first output terminal CCO 1 of the ⁇ uk converter and the second output terminal CCO 2 of the ⁇ uk converter.
- the negative input terminal IT 2 is grounded. Therefore, the second output terminal BCO 2 of the boost converter, the first output terminal CCO 1 of the ⁇ uk converter, and the intermediate output terminal OT 3 are also grounded. Further, a point between the emitter of the first controllable switch S 1 and the emitter of the second controllable switch S 2 is grounded, a point between series-connected first capacitor C 1 and second capacitor C 2 is grounded, and a cathode of the second diode D 2 is grounded.
- the output voltage u out is a sum of the output voltage u 1 of the boost converter and the output voltage u 2 of the ⁇ uk converter.
- Voltages u 1 and u 2 may be regulated independently according to equations ⁇ 1 ⁇ and ⁇ 2 ⁇ below.
- Voltage u 1 can be controlled by adjusting the duty-cycle DS 1 of switch S 1 according to equation ⁇ 1 ⁇ .
- the duty-cycle DS 2 of switch S 2 can be controlled according to equation ⁇ 2 ⁇ in order to regulate voltage u 2 .
- the non-isolated DC-DC converter assembly of FIG. 3 has a current source input characteristic, whereby the current absorbed from the power supply, such as the photovoltaic cell means PVM, is continuous.
- a ripple peakto-peak value of the current absorbed from the photovoltaic cell means PVM is dependent on the inductances of the first inductor L 1 and second inductor L 2 .
- the first controllable switch S 1 and the second controllable switch S 2 are IGBTs (Insulated Gate Bipolar Transistors), but one skilled in the art would understand that other types of controllable switches may also be used as the first controllable switch S 1 and the second controllable switch S 2 .
- FIG. 4 shows a simplified circuit diagram of a solar power station including photovoltaic cell means PVM, the non-isolated DC-DC converter assembly of FIG. 3 , and a half-bridge inverter HBI.
- the connection between the photovoltaic cell means PVM and the non-isolated DC-DC converter assembly is identical to the connection in FIG. 3 .
- the half-bridge inverter HBI connected to the DC-DC converter assembly can be a known two-level half-bridge inverter, for example.
- the half-bridge inverter HBI is connected to an electrical power network GD.
- the half-bridge inverter HBI includes a third controllable switch S 3 , a third diode D 3 , a fourth controllable switch S 4 , and a fourth diode D 4 .
- the third controllable switch S 3 and the fourth controllable switch S 4 are connected in series between the positive output terminal OT 1 and the negative output terminal OT 2 .
- the third diode D 3 is connected anti-parallel with the third controllable switch S 3 .
- the fourth diode D 4 is connected anti-parallel with the fourth controllable switch S 4 .
- the electrical power network GD has a first grid terminal GDT 1 and a second grid terminal GDT 2 .
- the first grid terminal GDT 1 is connected between the emitter of the third controllable switch S 3 and the collector of the fourth controllable switch S 4 .
- the second grid terminal GDT 2 is connected to the intermediate output terminal OT 3 .
- the negative input terminal IT 2 and the intermediate output terminal OT 3 are connected with a conductor having neither active nor passive components. Therefore, in operating conditions, the second grid terminal GDT 2 and the negative input terminal IT 2 are at the same electric potential. Consequently, the second grid terminal GDT 2 is earthed via the ground connection adjacent the negative terminal of the photovoltaic cell CPV.
- a solar power station is to be interpreted broadly. The expression is not limited to systems adapted to capture energy exclusively from sunlight. Instead, the light or other energy may originate, for example, from some industrial process or from any other source. Further, the nominal power of the solar power station is not limited in any way. Therefore, a solar power station may be a device capable of generating couple of watts or a huge scale power plant having nominal output of several gigawatts.
- the electrical power network GD represents the load of the half-bridge inverter HBI, and therefore also the load of the entire inverter assembly including the non-isolated DC-DC converter assembly and the half-bridge inverter HBI.
- the electrical power network GD represents the load of the half-bridge inverter HBI, and therefore also the load of the entire inverter assembly including the non-isolated DC-DC converter assembly and the half-bridge inverter HBI.
- a DC-DC converter assembly may be connected to an electrical power network by another type of half-bride inverter instead of a two-level half-bridge inverter.
- the DC-DC converter assembly may be connected to the grid by a known half-bridge three-level NPC inverter, for example. It is also possible to use a higher level half-bridge inverter such as a five-level half-bridge inverter, for example.
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Abstract
A non-isolated DC-DC converter assembly includes a boost converter and a Ćuk converter connected together in a specific way. The non-isolated DC-DC converter assembly allows for grounding of a source and load at the same time, and provides a complete adjustability of the output voltage of the non-isolated DC-DC converter. Further, the DC-DC converter assembly of the disclosure has a current source input characteristic, whereby the current absorbed from the power supply is continuous
Description
- This application claims priority under 35 U.S.C. §119 to European Patent Application No. 09174753.5 filed in Europe on Nov. 2, 2009, the entire content of which is hereby incorporated by reference in its entirety.
- The present disclosure relates to a non-isolated DC-DC converter assembly, such as a non-isolated DC-DC converter assembly which is suitable for use with a photovoltaic cell, for example.
- Nowadays, there are generally two main groups of photovoltaic (PV) inverters, namely isolated and non-isolated. Due to the galvanic isolation, the isolated inverters allow the photovoltaic panel terminal to be grounded, which is mandatory in some countries due to safety issues relating to leakage current. Grounding the negative photovoltaic panel terminal is also advantageous because it alleviates degradation problems of the photovoltaic panels. Even in countries where the galvanic isolation is not mandatory, the presence of the transformer is required when some photovoltaic cell technologies, e.g. thin-film, are employed. However, this extra component, e.g., the transformer, when operating at a low frequency, increases the overall volume, weight and cost of the system. In order to overcome that, the low frequency transformer has been replaced by high-frequency transformers operating in an intermediary isolated dc-dc converter. Nevertheless, this alternative generally results in a more complex system configuration as well as additional costs due to the higher number of active and passive devices. Due to these limitations, emphasis has been given to photovoltaic inverters without any kind of transformer, which are called non-isolated PV inverters. This family of converters is able to provide higher efficiency with low size and volume. Also, manufacturing costs may be lower. However, it still has to comply with safety and degradation issues. Therefore, non-isolated PV inverters require a dedicated topology either on the dc-dc converter side or on the inverter side.
- A known photovoltaic inverter assembly includes a boost converter connected to a full-bridge inverter. The boost converter boosts the voltage generated by a photovoltaic string to a level which is necessary for the inverter to transfer the power to the grid. However, although the boost converter has advantages, such as a low number of components and simplicity, it has some disadvantages with regard to the connection with the above-mentioned photovoltaic inverter assembly. If the full-bridge inverter operates under a unipolar modulation, which has a higher efficiency as compared to bipolar modulation, a parasitic capacitance existing between the negative terminal of the photovoltaic string and ground creates a path to a common-mode current to circulate. This common-mode current will superimpose the load current causing EMI, safety and degradation problems.
- In published patent application U.S. 2004/0164557, entitled “Monopolar DC to Bipolar to AC Converter”, a DC-DC converter is proposed which permits the source and load to be grounded at the same time. The output voltage of the DC-DC converter proposed in U.S. 2004/0164557 cannot be regulated. In operating situations where the voltage generated by the source of the DC-DC converter is below the level requested by the load, the converter has to shutdown, thereby reducing system availability. Further, since the DC-DC converter of U.S. 2004/0164557 includes a buck-boost converter, the source will suffer from a pulsating current.
- An exemplary embodiment provides a non-isolated DC-DC converter assembly which includes a positive input terminal, a negative input terminal, a positive output terminal, and a negative output terminal. The exemplary DC-DC converter assembly includes a boost converter having a first input terminal, a second input terminal, a first output terminal and a second output terminal. The exemplary DC-DC converter assembly also includes an intermediate output terminal, and a Ćuk converter, which includes a first input terminal, a second input terminal, a first output terminal and a second output terminal. The first input terminal of the boost converter and the second input terminal of the Ćuk converter are conductively connected to the positive input terminal. The second input terminal of the boost converter and the first input terminal of the Ćuk converter are conductively connected to the negative input terminal. The first output terminal of the boost converter is conductively connected to the positive output terminal. The second output terminal of the Ćuk converter is conductively connected to the negative output terminal. The second output terminal of the boost converter and the first output terminal of the Ćuk converter are conductively connected to the intermediate output terminal. The negative input terminal and the intermediate output terminal are configured to be grounded.
- Additional refinements, advantages and features of the present disclosure are described in more detail below with reference to exemplary embodiments illustrated in the drawings, in which:
-
FIG. 1 shows a known boost converter; -
FIG. 2 shows a known Ćuk converter; -
FIG. 3 shows an exemplary embodiment of a non-isolated DC-DC converter assembly connected to a photovoltaic cell, according to an embodiment of the present disclosure; and -
FIG. 4 shows a simplified circuit diagram of a solar power station including the exemplary converter assembly ofFIG. 3 . - Exemplary embodiments of the present disclosure provide a non-isolated dc-dc converter which allows grounding the negative terminal of the photovoltaic modules, avoiding any safety or degradation issue caused by leakage current flowing in existing parasitic capacitors.
- According to an exemplary embodiment, the non-isolated DC-DC converter assembly includes a boost converter and a Ćuk converter connected together in a specific way.
- According to an exemplary embodiment, the non-isolated DC-DC converter assembly allows for grounding of a source and load at the same time. In accordance with exemplary embodiments of the present disclosure, a complete adjustability of the output voltage of the non-isolated DC-DC converter is achieved. Further, the DC-DC converter assembly of the disclosure has current source input characteristic, whereby the current absorbed from the power supply is continuous.
- The converter assembly according to exemplary embodiments of the present disclosure can be installed using any kind of photovoltaic cell technologies without of the drawback of low efficiency, large volume and high cost associated with isolated photovoltaic converters. The possibility of grounding the power supply and the load at the same time allows removing the bulky transformer while still avoiding any EMI aspects caused by the presence of a common-mode current flowing through parasitic components.
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FIG. 1 shows a conventional boost converter configured to step up input voltage into higher output voltage. The boost converter includes an inductor L1′, a diode D1′ and a controllable switch S1′. The boost converter has a first input terminal BCI1′, a second input terminal BCI2′, a first output terminal BCO1′ and a second output terminal BCO2′. The input direct voltage is inputted through the first input terminal BCI1′ and the second input terminal BCI2′. The first input terminal BCI1′ is a positive terminal, and the second input terminal BCI2′ is a negative terminal. The output voltage is present between the first output terminal BCO1′ and the second output terminal BCO2′. The first output terminal BCO1′ is a positive terminal, and the second output terminal BCO2′ is a negative terminal. - The inductor L1′ and the diode D1′ are connected in series between the first input terminal BCI1′ of the boost converter and the first output terminal BCO1′ of the boost converter. The cathode of the diode D1′ is connected to the first output terminal BCO1′. The collector of the controllable switch S1′ is connected between the inductor L1′ and the anode of the diode D1′, and the emitter of the controllable switch S1′ is connected between the second input terminal BCI2′ and the second output terminal BCO2′. The second input terminal BCI2′ and the second output terminal BCO2′ are connected with a conductor having neither active nor passive components. Therefore, the second input terminal BCI2′ and the second output terminal BCO2′ are, in operating conditions, substantially at the same electric potential.
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FIG. 2 shows a known Ćuk converter. The Ćuk converter is capable of stepping up and stepping down its input voltage. The Ćuk converter includes inductors L2′ and L3′, a diode D2′, a controllable switch S2′, and capacitors C2′ and C3′. The Ćuk converter has a first input terminal CCI1′, a second input terminal CCI2′, a first output terminal CCO1′ and a second output terminal CCO2′. The input direct voltage is inputted through the first input terminal CCI1′ and the second input terminal CCI2′. The output voltage is present between the first output terminal CCO1′ and the second output terminal CCO2′. - The Ćuk converter of
FIG. 2 is an inverting converter, which means that the output voltage is negative with respect to the input voltage. This means that if an operator wants the first output terminal CCO1′ of the Ćuk converter to be the positive one, then the second input terminal CCI2′ must be connected to a higher electrical potential than the first input terminal CCI1′ of the Ćuk converter. - The inductor L2′, the capacitor C3′ and the inductor L3′ are connected in series between the second input terminal CCI2′ of the Ćuk converter and the second output terminal CCO2′ of the Ćuk converter such that the capacitor C3′ is located electrically between the inductor L2′ and the inductor L3′. The inductor L2′ is connected between the second input terminal CCI2′ and the capacitor C3′, and the inductor L3′ is connected between the second output terminal CCO2′ and the capacitor C3′.
- A collector of the controllable switch S2′ is connected between the inductor L2′ and the capacitor C3′, and the emitter of the controllable switch S2′ is connected between the first input terminal CCI1′ and the first output terminal CCO1′. The first input terminal CCI1′ and the first output terminal CCO1′ of the Ćuk converter are connected with a conductor having neither active nor passive components. Therefore, the first input terminal CCI1′ and the first output terminal CCO1′ are, in operating conditions, substantially at the same electric potential.
- The anode of the diode D2′ is connected between the capacitor C3′ and the inductor L3′. The cathode of the diode D2′ is connected between the first input terminal CCI1′ and the first output terminal CCO1′.
- The capacitor C2′ is connected between the first output terminal CCO1′ and the second output terminal CCO2′. Therefore the voltage of the capacitor C2′ is equal to the output voltage of the Ćuk converter.
-
FIG. 3 shows a non-isolated DC-DC converter assembly according to an exemplary embodiment of the present disclosure connected to a photovoltaic cell means (PVM) having a photovoltaic cell CPV. The photovoltaic cell CPV is configured to convert solar energy into direct current (DC). The photovoltaic cell CPV is configured to generate a direct voltage uin, which is the input voltage of the non-isolated DC-DC converter assembly. The photovoltaic cell CPV can be based on any known photovoltaic cell technology. - The converter assembly according to exemplary embodiments of the present disclosure includes features of the boost converter shown in
FIG. 1 and the Ćuk converter shown inFIG. 2 . For example, according to an exemplary embodiment depicted inFIG. 3 , the converter assembly is a combination of the boost converter shown inFIG. 1 and the Ćuk converter shown inFIG. 2 . The converter assembly has a positive input terminal IT1, a negative input terminal IT2, a positive output terminal OT1 and a negative output terminal OT2. The input voltage of the converter assembly is present between the positive input terminal IT1 and the negative input terminal IT2. The boost converter and the Ćuk converter are connected such that the output voltage uout of the converter assembly present between the positive output terminal OT1 and the negative output terminal OT2 is substantially a sum of the absolute values of output voltages of the boost converter and the Ćuk converter. - According to an exemplary embodiment, the non-isolated DC-DC converter assembly of
FIG. 3 includes all the components in the boost converter ofFIG. 1 and in the Ćuk converter ofFIG. 2 . Reference signs used inFIG. 3 correspond to those used inFIGS. 1 and 2 with the exception that apostrophes (') have been removed. - The boost converter of
FIG. 3 has a first input terminal BCI1, a second input terminal BCI2, a first output terminal BCO1 and a second output terminal BCO2. The output voltage u1 of the boost converter is present between the first output terminal BCO1 and the second output terminal BCO2. The Ćuk converter ofFIG. 3 has a first input terminal CCI1, a second input terminal CCI2, a first output terminal CCO1 and a second output terminal CCO2. The output voltage u2 of the Ćuk converter is present between the first output terminal CCO1 and the second output terminal CCO2. The output voltage uout of the non-isolated DC-DC converter assembly ofFIG. 3 is a sum of the output voltage u1 of the boost converter and the output voltage u2 of the Ćuk converter. - The first input terminal BCI1 of the boost converter and the second input terminal CCI2 of the Ćuk converter are conductively connected to the positive input terminal IT1 such that, in operating situations, the first input terminal BCI1, the second input terminal CCI2, and the positive input terminal are at the same electric potential. The second input terminal BCI2 of the boost converter and the first input terminal CCI1 of the Ćuk converter are conductively connected to the negative input terminal IT2 such that, in operating situations, the second input terminal BCI2, the first input terminal CCI1, and the negative input terminal IT2 are at the same electric potential. The first output terminal BCO1 of the boost converter is conductively connected to the positive output terminal OT1 such that, in operating situations, the first output terminal BCO1 and the positive output terminal OT1 are at the same electric potential. The second output terminal CCO2 of the Ćuk converter is conductively connected to the negative output terminal OT2 such that, in operating situations, the second output terminal CCO2 and the negative output terminal OT2 are at the same electric potential.
- The converter assembly of
FIG. 3 has an intermediate output terminal OT3, which is conductively connected to the second output terminal BCO2 of the boost converter and the first output terminal CCO1 of the Ćuk converter. Since there are neither active nor passive components between the intermediate output terminal OT3 and the negative input terminal IT2, these two terminals are, in operating situations, at the same electric potential. - The boost converter of
FIG. 3 includes a first inductor L1, a first diode D1, a first controllable switch S1 and a first capacitor C1. The first inductor L1 and the first diode D1 are connected in series between the first input terminal BCI1 of the boost converter and the first output terminal BCO1 of the boost converter. The cathode of the first diode D1 is connected to the first output terminal BCO1 of the boost converter. The first controllable switch S1 is located electrically between a point situated electrically between the first inductor L1 and the first diode D1, and a point situated electrically between the second input terminal BCI2 of the boost converter and the second output terminal BCO2 of the boost converter. The collector of the first controllable switch S1 is connected between the first inductor L1 and the anode of the first diode D1. The first capacitor C1 is connected between the first output terminal BCO1 of the boost converter and the second output terminal BCO2 of the boost converter. - It is to be noted that in the boost converter of
FIG. 1 there is no first capacitor C1 or any equivalent component. There are no further additional components in the converter assembly ofFIG. 3 . All other components of the converter assembly ofFIG. 3 are present in the boost converter ofFIG. 1 and in the Ćuk converter ofFIG. 2 . - The Ćuk converter of
FIG. 3 includes a second inductor L2, a third inductor L3, a second diode D2, a second controllable switch S2, a second capacitor C2 and a third capacitor C3. The second inductor L2, the third capacitor C3 and the third inductor L3 are connected in series between the second input terminal CCI2 of the Ćuk converter and the second output terminal CCO2 of the Ćuk converter such that the third capacitor C3 is located electrically between the second inductor L2 and the third inductor L3. The second controllable switch S2 is located electrically between a point situated electrically between the second inductor L2 and the third capacitor C3, and a point situated electrically between the first input terminal CCI1 of the Ćuk converter and the first output terminal CCO1 of the Ćuk converter. The collector of the second controllable switch S2 is connected between the second inductor L2 and the third capacitor C3. The second diode D2 is located electrically between a point situated electrically between the third capacitor C3 and the third inductor L3, and a point situated electrically between the first input terminal CCI1 of the Ćuk converter and the first output terminal CCO1 of the Ćuk converter. The anode of the second diode D2 is connected between the third capacitor C3 and the third inductor L3. The cathode of the second diode D2 is connected between the first input terminal CCI1 and the first output terminal CCO1. The second capacitor C2 is located electrically between the first output terminal CCO1 of the Ćuk converter and the second output terminal CCO2 of the Ćuk converter. - The negative input terminal IT2 is grounded. Therefore, the second output terminal BCO2 of the boost converter, the first output terminal CCO1 of the Ćuk converter, and the intermediate output terminal OT3 are also grounded. Further, a point between the emitter of the first controllable switch S1 and the emitter of the second controllable switch S2 is grounded, a point between series-connected first capacitor C1 and second capacitor C2 is grounded, and a cathode of the second diode D2 is grounded.
- As mentioned above, the output voltage uout is a sum of the output voltage u1 of the boost converter and the output voltage u2 of the Ćuk converter. Voltages u1 and u2 may be regulated independently according to equations {1} and {2} below. Voltage u1 can be controlled by adjusting the duty-cycle DS1 of switch S1 according to equation {1}. The duty-cycle DS2 of switch S2 can be controlled according to equation {2} in order to regulate voltage u2.
-
- The non-isolated DC-DC converter assembly of
FIG. 3 has a current source input characteristic, whereby the current absorbed from the power supply, such as the photovoltaic cell means PVM, is continuous. A ripple peakto-peak value of the current absorbed from the photovoltaic cell means PVM is dependent on the inductances of the first inductor L1 and second inductor L2. - In the exemplary embodiments discussed above, the first controllable switch S1 and the second controllable switch S2 are IGBTs (Insulated Gate Bipolar Transistors), but one skilled in the art would understand that other types of controllable switches may also be used as the first controllable switch S1 and the second controllable switch S2.
-
FIG. 4 shows a simplified circuit diagram of a solar power station including photovoltaic cell means PVM, the non-isolated DC-DC converter assembly ofFIG. 3 , and a half-bridge inverter HBI. The connection between the photovoltaic cell means PVM and the non-isolated DC-DC converter assembly is identical to the connection inFIG. 3 . The half-bridge inverter HBI connected to the DC-DC converter assembly can be a known two-level half-bridge inverter, for example. The half-bridge inverter HBI is connected to an electrical power network GD. The half-bridge inverter HBI includes a third controllable switch S3, a third diode D3, a fourth controllable switch S4, and a fourth diode D4. The third controllable switch S3 and the fourth controllable switch S4 are connected in series between the positive output terminal OT1 and the negative output terminal OT2. The third diode D3 is connected anti-parallel with the third controllable switch S3. The fourth diode D4 is connected anti-parallel with the fourth controllable switch S4. - The electrical power network GD has a first grid terminal GDT1 and a second grid terminal GDT2. The first grid terminal GDT1 is connected between the emitter of the third controllable switch S3 and the collector of the fourth controllable switch S4. The second grid terminal GDT2 is connected to the intermediate output terminal OT3. The negative input terminal IT2 and the intermediate output terminal OT3 are connected with a conductor having neither active nor passive components. Therefore, in operating conditions, the second grid terminal GDT2 and the negative input terminal IT2 are at the same electric potential. Consequently, the second grid terminal GDT2 is earthed via the ground connection adjacent the negative terminal of the photovoltaic cell CPV.
- Herein, the expression “solar power station” is to be interpreted broadly. The expression is not limited to systems adapted to capture energy exclusively from sunlight. Instead, the light or other energy may originate, for example, from some industrial process or from any other source. Further, the nominal power of the solar power station is not limited in any way. Therefore, a solar power station may be a device capable of generating couple of watts or a huge scale power plant having nominal output of several gigawatts.
- In the circuit diagram of
FIG. 4 , the electrical power network GD represents the load of the half-bridge inverter HBI, and therefore also the load of the entire inverter assembly including the non-isolated DC-DC converter assembly and the half-bridge inverter HBI. One skilled in the art would understand that it is possible to connect a variety of different loads to the half bridge inverter. - In accordance with another exemplary embodiment, a DC-DC converter assembly may be connected to an electrical power network by another type of half-bride inverter instead of a two-level half-bridge inverter. The DC-DC converter assembly may be connected to the grid by a known half-bridge three-level NPC inverter, for example. It is also possible to use a higher level half-bridge inverter such as a five-level half-bridge inverter, for example.
- It will be appreciated by those skilled in the art that the present invention can be embodied in other specific forms without departing from the spirit or essential characteristics thereof. The presently disclosed embodiments are therefore considered in all respects to be illustrative and not restricted. The scope of the invention is indicated by the appended claims rather than the foregoing description and all changes that come within the meaning and range and equivalence thereof are intended to be embraced therein.
Claims (9)
1. A non-isolated DC-DC converter assembly comprising:
a positive input terminal;
a negative input terminal;
a positive output terminal;
a negative output terminal;
a boost converter including a first input terminal, a second input terminal, a first output terminal and a second output terminal;
an intermediate output terminal; and
a Ćuk converter including a first input terminal, a second input terminal, a first output terminal and a second output terminal, wherein:
the first input terminal of the boost converter and the second input terminal of the Ćuk converter are conductively connected to the positive input terminal;
the second input terminal of the boost converter and the first input terminal of the Ćuk converter are conductively connected to the negative input terminal;
the first output terminal of the boost converter is conductively connected to the positive output terminal;
the second output terminal of the Ćuk converter is conductively connected to the negative output terminal;
the second output terminal of the boost converter and the first output terminal of the Ćuk converter are conductively connected to the intermediate output terminal; and
the negative input terminal and the intermediate output terminal are configured to be grounded.
2. A converter assembly according to claim 1 , wherein the negative input terminal and the intermediate output terminal are conductively connected to each other.
3. A converter assembly according to claim 1 , wherein:
the boost converter comprises a first inductor, a first diode, a first controllable switch and a first capacitor;
the first inductor and the first diode is connected in series between the first input terminal of the boost converter and the first output terminal of the boost converter;
the first controllable switch is located electrically between a point situated electrically between the first inductor and the first diode, and a point situated electrically between the second input terminal of the boost converter and the second output terminal of the boost converter; and
the first capacitor is located electrically between the first output terminal of the boost converter and the second output terminal of the boost converter.
4. A converter assembly according to claim 1 , wherein:
the Ćuk converter comprises a second inductor, a third inductor, a second diode, a second controllable switch, a second capacitor and a third capacitor;
the second inductor, the third capacitor and the third inductor are connected in series between the second input terminal of the Ćuk converter and the second output terminal of the Ćuk converter such that the third capacitor is located electrically between the second inductor and the third inductor;
the second controllable switch is located electrically between a point situated electrically between the second inductor and the third capacitor, and a point situated electrically between the first input terminal of the Ćuk converter and the first output terminal of the Ćuk converter;
the second diode is located electrically between a point situated electrically between the third capacitor and the third inductor, and a point situated electrically between the first input terminal of the Ćuk converter and the first output terminal of the Ćuk converter; and
the second capacitor is located electrically between the first output terminal of the Ćuk converter and the second output terminal of the Ćuk converter.
6. A solar power station comprising:
photovoltaic cell means having at least one photovoltaic cell configured to convert solar energy into direct current; and
the converter assembly according to claim 1 ,
wherein the at least one photovoltaic cell is connected between the positive input terminal and the negative input terminal of the converter assembly.
7. An inverter assembly comprising:
a half-bridge inverter; and
the non-isolated DC-DC converter assembly as claimed in claim 1 ,
wherein the half-bridge inverter is connected between the positive output terminal and the negative output terminal, and the intermediate output terminal is configured to be connected to a load of the half-bridge inverter.
8. A converter assembly according to claim 2 , wherein:
the boost converter comprises a first inductor, a first diode, a first controllable switch and a first capacitor;
the first inductor and the first diode are connected in series between the first input terminal of the boost converter and the first output terminal of the boost converter;
the first controllable switch is located electrically between a point situated electrically between the first inductor and the first diode, and a point situated electrically between the second input terminal of the boost converter and the second output terminal of the boost converter; and
the first capacitor is located electrically between the first output terminal of the boost converter and the second output terminal of the boost converter.
9. A converter assembly according to claim 3 , wherein:
the Ćuk converter comprises a second inductor, a third inductor, a second diode, a second controllable switch, a second capacitor and a third capacitor;
the second inductor, the third capacitor and the third inductor are connected in series between the second input terminal of the Ćuk converter and the second output terminal of the Ćuk converter such that the third capacitor is located electrically between the second inductor and the third inductor;
the second controllable switch is located electrically between a point situated electrically between the second inductor and the third capacitor, and a point situated electrically between the first input terminal of the Ćuk converter and the first output terminal of the Ćuk converter;
the second diode is located electrically between a point situated electrically between the third capacitor and the third inductor, and a point situated electrically between the first input terminal of the Ćuk converter and the first output terminal of the Ćuk converter; and
the second capacitor is located electrically between the first output terminal of the Ćuk converter and the second output terminal of the Ćuk converter.
10. A converter assembly according to claim 9 , wherein a point between the emitter of the first controllable switch and the emitter of the second controllable switch, a point between series-connected first capacitor and second capacitor, and a cathode of the second diode are, in operating situations substantially at the same electric potential as the negative input terminal.
Applications Claiming Priority (2)
Application Number | Priority Date | Filing Date | Title |
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EP09174753A EP2317635A1 (en) | 2009-11-02 | 2009-11-02 | Non-isolated DC-DC converter assembly |
EP09174753.5 | 2009-11-02 |
Publications (1)
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US20110103118A1 true US20110103118A1 (en) | 2011-05-05 |
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ID=41796131
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US12/917,879 Abandoned US20110103118A1 (en) | 2009-11-02 | 2010-11-02 | Non-isolated dc-dc converter assembly |
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US (1) | US20110103118A1 (en) |
EP (1) | EP2317635A1 (en) |
CN (1) | CN102055316B (en) |
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US20140001867A1 (en) * | 2012-06-29 | 2014-01-02 | Cyber Power Systems Inc. | Method for controlling a grid-connected power supply system |
US20140217827A1 (en) * | 2013-02-01 | 2014-08-07 | 3L Power Llc | Apparatus for and method of operation of a power inverter system |
US20150244259A1 (en) * | 2014-02-21 | 2015-08-27 | Airbus Operations Gmbh | Bipolar high-voltage network and method for operating a bipolar high-voltage network |
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Also Published As
Publication number | Publication date |
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CN102055316B (en) | 2014-03-12 |
EP2317635A1 (en) | 2011-05-04 |
CN102055316A (en) | 2011-05-11 |
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